1. Field of the Disclosure
The present disclosure relates to a photoelectric device having Group III nitride semiconductor, and more particularly to the light emitting structure of a photoelectric device.
2. Description of the Related Art
Light emitting diodes of gallium nitride or other Group III nitride semiconductor materials are built upon a sapphire substrate mainly due to a high degree of lattice compatibility therebetween (although a buffer layer is still often required to improve the match). However, sapphire substrates have many disadvantages, such as high insulation characteristics, and due to such characteristics it is not easy to create a light emitting diode made of Group III nitride semiconductor material having a vertical conductive structure. Therefore, technology continues to advance and allow use of other substrate materials, such as silicon carbide, to reduce such disadvantages.
Due to its high conductivity, silicon carbide can be used to produce a conductive substrate. Moreover, due to its high stability, silicon carbide is becoming more important in such manufacturing processes. Although a Group III nitride semiconductor layer can be deposited on a silicon carbide substrate with the help of a buffer layer made of gallium nitride or aluminum gallium nitride, the degree of lattice match between a Group III nitride semiconductor material and silicon carbide is still lower than the degree of lattice match between aluminum gallium nitride and silicon carbide. The lattice mismatch often causes defects in an epitaxial layer even where the buffer layer is formed on a silicon carbide substrate. Furthermore, a silicon carbide substrate is more expensive than substrates made of other materials.
FIG. 1A and FIG. 1B show a method of separating a thin film from a growth substrate, disclosed in U.S. Pat. No. 6,071,795. The method initially forms a separation region 12 and a silicon nitride layer 13 on a sapphire substrate 11, and then a bonding layer 14 is disposed on the surface of the silicon nitride layer 13. Next, with the help of the bonding layer 14, a silicon substrate 15 is bonded to the sapphire substrate 11 with a stacked-layer structure. A laser beam penetrating the sapphire substrate 11 is directed at the separation region 12, generates decomposition thereof. Finally, the remnant material of the decomposed separation region 12 is cleared to obtain a composite including the silicon substrate 15 and the silicon nitride layer 13. However, because the bonding layer 14 between the silicon substrate 15 and the silicon nitride layer 13 is dielectric, the composite cannot be a basis for building a vertical structure light emitting diode. Moreover, if the material for the bonding layer 14 is disposed incorrectly or selected improperly, the bonding is affected, and defects are formed in the silicon nitride layer 13.
FIG. 2 shows a method of separating two layers of material from one another, disclosed in U.S. Pat. No. 6,740,604. The technology used for the disclosure related to FIG. 2 is similar to that for the disclosure related to FIG. 1A and FIG. 1B. A laser beam 23 is directed at the interface between a first semiconductor layer 21 and a second semiconductor layer 22, and initiates the decomposition of the second semiconductor layer 22 at the interface. Finally, the first semiconductor layer 21 is separated from the second semiconductor layer 22. The second semiconductor layer 22 can be the film layer formed on a substrate. In such process, a substrate replaces the first semiconductor layer 21, and then both are separated.
FIG. 3 shows a structure prior to separation of the substrate, disclosed in U.S. Pat. No. 6,746,889. The method initially grows several epitaxial layers, which include the first region 32 of a first conductivity type, a light-emitting p-n junction 33, and the second region 34 of a second conductivity type, on a substrate 31. Next, several scribe lines 36 are cut through the epitaxial layers of the first region 32, light-emitting p-n junction 33 and second region 34 to form multiple individual optoelectronic devices or dies 35 on the substrate 31. Thereafter, the second region 34 is bonded to a submount 37. As shown, a laser beam, in the same manner, penetrating the substrate 31 causes the substrate 31 to separate from the first region 32. Separated optoelectronic devices or dies 35 can be removed from the submount 37 and proceed through the packaging processes. Obviously, when the epitaxial layers are cut through, individual optoelectronic devices or dies 35 bonded to the submount 37 squeeze one another by external forces such that die cracks may occur.
FIG. 4 is a side view of the laser lift-off process for removing a sapphire substrate, disclosed in U.S. Pat. No. 6,617,261. A gallium nitride layer 42 is initially formed on a sapphire substrate 41, and then multiple grooves 44 are formed by etching process. Next, a silicon substrate 43 is bonded to the surface where the gallium nitride layer 42 is formed and then is etched to form the grooves 44. Thereafter, an ultraviolet excimer laser 45 emits a laser beam 46 to the sapphire substrate 41. The laser beam 46 penetrates the transparent sapphire substrate 41 to cause the gallium nitride to decompose at the interface so as to obtain a silicon substrate 43 bonded with the gallium nitride layer 42. Any residual gallium metal on the surface of the gallium nitride layer 42 is removed by hydrochloric acid. The gallium nitride layer 42 is finally cleaned for subsequent deposition processes.
Conventional technologies use high-energy laser beams to separate substrates or light emitting dies. However, those technologies have low throughput and require expensive equipment. Therefore, a separation technology guaranteeing the quality of produced light emitting dies, and can be applied to mass production with acceptable throughput and minimized cost is required.